Groundwater Plume Analytics™

Evaluation of the relative stability of a groundwater contaminant plume is generating increasing attention as many domestic and international stakeholders are realizing the applicability of plume stability as part of the environmental evaluation and/or remedial planning process of a site. This is especially important in the development of a long-term risk management strategy for a site. A plume stability evaluation allows the stakeholder to assess whether a contaminant plume is stable, decreasing, or increasing for a variety of metrics (i.e., area, concentration, mass, center of mass, and spread of mass). This allows better evaluation of whether additional remedial action is necessary, if risk-based closure of a site is applicable, or whether natural attenuation processes may be occurring at a site.

Groundwater plume analytics refers to the use of innovative evaluation techniques and methods to reliably and effectively communicate meaningful patterns in environmental data. Analytics relies primarily on graphical displays to communicate insight. The Ricker Method® for plume stability analysis is a unique method of evaluating plume stability that overcomes limitations posed by conventional well-by-well analysis techniques.

Outputs from the Ricker Method® can be used as a basis for primary analysis and other plume diagnostic tools that allow the user to further evaluate and communicate groundwater plume dynamics. This method has been used as a basis for the cessation of remediation systems, evaluation of remediation progress, identification of commingled plumes, identification of potential unrealized source areas, and providing additional lines of evidence for natural attenuation; examples of which will be presented. This session will also present certain aspects of proprietary analysis tools including Remediation System Benefit Analysis (RSBA®), Spatial Change Indicator™ (SCI) analysis, and Well Sufficiency Analysis™.

RSBA® is an interpretation of the relative benefit of a remediation system based on graphical data outputs created from the Ricker Method® evaluation and additional data inputs. In effect, what RSBA® does is evaluate the efficiency of an active groundwater remediation system that removes contaminant mass from groundwater (e.g., pump and treat). The tool evaluates whether an active system may be considered efficient or inefficient based on an evaluation of contaminant mass removed via the system and the relative stability of a groundwater plume.

The Spatial Change Indicator™ evaluation shows relative changes in the plume over time. For this analysis, each plume map in a particular time period is compared to the first plume map in the series. The current plume is subtracted from the original plume to create a new isopleth map that shows areas of the plume that decreased in concentration (indicated by blue shading), increased in concentration (indicated by red shading), or did not change (indicated by clear or no shading). The visual aspect of this analysis allows the viewer to observe patterns of plume behavior over time.

The Ricker Method® Well Sufficiency Analysis™ is a statistical method to determine if a monitoring well network can be reduced while maintaining confidence in the ability of the network to monitor plume behavior. The analysis uses the plume stability characteristics of area, average concentration and mass indicator from the entire network as a baseline to compare the respective plume stability characteristics from a reduced, or optimized, network. These comparisons are made for each of the plume stability characteristics using Mann-Kendall trend, linear regression trend, average relative percent difference and correlation coefficient. The optimized network is then assigned an overall strength based on the results of the comparisons made in each of the plume stability characteristics.

Multiple plume analytics tools derived from the Ricker Method® will be presented; however, the session will also focus on these tools as they apply to chlorinated constituent sites. It is useful when assessing chlorinated volatile organic compound (CVOC) data to also evaluate the data on a molar basis. This is especially important for evaluating the degradation of parent-daughter sequences such as the chlorinated ethenes and ethanes. For example, during reductive dechlorination the relative molar fraction of parent compounds progressively decreases through time and the fraction of daughter compounds progressively increases. Further, when a parent compound degrades to a daughter compound, the mass based concentration of “total CVOCs” decreases because one chlorine atom is released in each sequential reaction. However, the number of moles does not decrease since one molecule of a parent compound (e.g., PCE) produces one molecule of its respective daughter compound (e.g., TCE) and so on. The molar concentration only decreases once the parent constituent has been completely mineralized to ultimate benign end products (i.e., carbon dioxide, water, and chloride ion). In addition to demonstrating complete mineralization of CVOC compounds, this is especially important for evaluating and detecting potential new, separate, and/or episodic release sources within a plume. Examples demonstrating the importance and use of evaluating data on a molar basis will be presented.

Primary Author/Conference Presenter:
Joe Ricker
Principal Engineer
EarthCon Consultants, Inc.
Memphis, Tennessee